1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling brakes which is suit able for use in an electric vehicle, wherein each of the brakes can efficiently be operated by controlling the braking ratio, or proportion of a regenerative braking function to a frictional braking function.
2. Description of the Related Art
In general, a regenerative brake is known which makes use of a regenerative operation of a drive motor and a mechanically-operated friction brake. An example of such a brake is a typical disk brake which is principally employed in an electric vehicle in order to decelerate the electric vehicle when running.
A regenerative brake is normally operated by lifting the foot off of an accelerator, whereas a friction brake is actuated by depressing a brake pedal. A battery is charged by feeding back or returning regenerative energy Produced by regenerative braking to the battery. In order to improve the efficiency of recovery, or withdrawal of the regenerative energy, it is necessary to cause the braking of the electric vehicle by the regenerative brake to take precedence over the braking of the electric vehicle by the friction brake. This has been disclosed in U.S. Pat. No. 3,621,929.
In a conventional brake control apparatus used for an electric vehicle, separate operation systems are provided for the regenerative brake and the friction brake, respectively as in the case where an accelerator pedal and a brake pedal are independently provided. Therefore, regenerative energy cannot efficiently be recovered. When the brake pedal is depressed, for example, the friction brake is applied to the vehicle so as to rapidly reduce the rotational speed of each of the wheels. Therefore, sufficient torque cannot be applied to the drive motor, which serves as a generator, so that recovery of the regenerative energy cannot efficiently be performed. At the same time, a sufficient braking force cannot be developed by the regenerative brake alone. Therefore, the braking of the vehicle is dependent almost entirely on the friction brake. In this case, any regenerative energy is radiated in the form of heat generated by the friction brake, so that it cannot be recovered. Accordingly, the effect of the regenerative energy cannot be enhanced.